1. Field of the Invention
The present invention relates to a measuring probe, in particular for a contactless vector network analysis system, having a housing and, arranged on the housing, at least one coupling structure which is designed to couple an RF signal out from a signal line.
2. Description of Related Art
The use of contactless loop-type measuring probes for detecting interfering emissions is known, particularly in the field of electromagnetic compatibility (EMC), from for example H. Whiteside, R. W. P. King “The loop antenna as a probe”, IEEE Transactions on Antennas and Propagation, Vol. 12, No. 3, pp. 291-297, May 1964, or M. Kanda, “An electromagnetic near-field sensor for simultaneous electric and magnetic-field measurements”, IEEE Transactions on Electromagnetic Compatibility, Vol. 26, No. 3, pp. 102-110, August 1984, or M. E. G. Upton, A. C. Marvin, “Improvements to an electromagnetic near-field sensor for simultaneous electric and magnetic field measurements”, IEEE Transactions on Electromagnetic Compatibility, Vol. 35, No. 1, pp. 96-98, February 1993.
it is also known for loop-type probes to be used in the production of directional couplers from, for example, K. W. Wagner “Induktionswirkung von Wanderwellen in Nachbarleitungen” [Inductive effect of travelling waves on neighboring lines], Elektronische Zeitschrift, Vol. 35, pp. 639-643, 677-680, 705-708, 1914; P. P. Lombardini, R. F. Schwartz, P. J. Kelly, “Criteria for the design of loop-type directional couplers for the L band,” IEEE Transactions on Microwave Theory and Techniques, Vol. 4, No. 4, pp. 234-239, October 1956; B. Maher, “An L-band loop-type coupler,” IEEE Transactions on Microwave Theory and Techniques,” Vol. 9, No. 4, pp. 362-363, July 1961; F. De Groote, J. Verspecht, C. Tsironis, D. Barataud and J.-P. Teyssier, “An improved coupling method for time domain load-pull measurements,” European Microwave Conference, Vol. 1, p. 4 et seq. October 2005 or K. Yhland, J. Stenarson, “Noncontacting measurement of power in microstrip circuits,” in 65th ARFTG, pp. 201-205, June 2006.
A directional coupler is a four-port device which generally comprises two lines which are coupled to one another. The job of the directional coupler is to separate the forward and backward waves on a line.
Rather than loop-type probes, probes that are also used in EMC technology and for characterizing electrical components are purely inductive or capacitive probes, as is known for example from T. Zelder, H. Eul, “Contactless network analysis with improved dynamic range using diversity calibration,” Proceedings of the 36th European Microwave Conference, Manchester UK, pp. 478-481, September 2006; T. Zelder, H. Rabe, H. Eul, “Contactless electromagnetic measuring system using conventional calibration algorithms to determine scattering parameters,” Advances in Radio Sciences—Kleinheubacher Berichte 2006, Vol. 5, 2007; T. Zelder, I. Rolfes, H. Eul, “Contactless vector network analysis using diversity calibration with capacitive and inductive coupled sources,” Advances in Radio Science—Kleinheubacher Berichte, Vol. 5, 2007, or J. Stenarson, K. Yhland, C. Wingqvist, “An in-circuit noncontacting measurement method for S-parameters and power in planar circuits,” IEEE Transactions on Microwave Theory and Techniques, Vol. 49, No. 12, pp. 2567-2572, December 2001.
A possible coupling structure for separating forward and backward waves is the loop-type directional coupler, which was described by P. P. Lombardini, R. F. Schwartz, P. J. Kelly in “Criteria for the design of loop-type directional couplers for the L band,” IEEE Transactions on Microwave Theory and Techniques, Vol. 4, No. 4, pp. 234-239, October 1956 and by B. Maher in “An L-band loop-type coupler,” IEEE Transactions on Microwave Theory and Techniques, Vol. 9, No. 4, pp. 362-363, July 1961.
A loop-type directional coupler comprises a conductor loop which is positioned above or in a waveguide. Waveguides of any desired kinds may be used in this case such as hollow guides, planar strip lines, or co-axial lines. There are a variety of uses for a loop-type directional coupler. F. De Groote, et al. (op. cit), for example, used a loop-type directional coupler as a component of a contactless measuring system in 2005 and Yhland, et al. (op. cit.), used one as a component of a contactless measuring system in 2006.
Scattering parameters of electrical components embedded in a complex circuit can be determined by contactless vector network analysis. This is described in for example T. Zelder, B. Geck, M. Wollitzer, I. Rolfes and H. Eul, “Contactless network analysis system for the calibrated measurement of the scattering parameters of planar two-port devices,” Proceedings of the 37th European Microwave Conference, Munich, Germany, pp. 246-249, October 2007. Compared with conventional methods of network analysis where contacts are used, the internal directional couplers of a network analyzer are replaced by contactless near-field measuring probes which are connected directly to the vectorial points of measurement of the analyzer.